The objectives of this research are the synthesis, the unequivocal characterization, and the initial biological screening of a series of 5-oxo and 7-oxopyrido(2,3-d)pyrimidine ribonucleosides that are structurally related to the pyrrolo(2,3-d)pyrimidine nucleoside antibiotics, tubercidin, toyocomycin, and sangivamycin. The synthesis will be approached using a combination of procedures including the preparation of the requisite pyrido (2,3-d) pyrimidine bases, sugar-base coupling methods, and interconversions at the nucleoside level. New methods for the synthesis of the 2-amino and 2-fluoro analogs of the target nucleosides will be investigated. Proof of structure will be based upon unequivocal synthetic methods. Proof of configuration will be determined by conversion to the 3-5'-cyclonucleoside. The target nucleosides and the 2-substituted analogs will be subjected to biological evaluation using two enzymatic assays and in vivo evaluation for antitumor activity. Stability of the nucleosides to the catabolic enzyme, adenosine deaminase, will be determined based upon the known inactivity of this enzyme towards the pyrrolo (2,3-d)-pyrimidine nucleosides. The requirement that these nucleosides will require biological activation to the nucleotide level similar to tubercidin, will be determined using the enzyme adenosine kinase. The results of the two enzymatic assays and the in vivo assay will be correlated with structural parameters within this series of nucleosides, which will allow some insight to be gained for these compounds to serve as viable alternatives to the many compounds of biological importance containing adenosine. Additionally, these compounds may serve as useful probes in the determination of the mechanism of cytotoxicity of the pyrrolo(2,3-d)pyrimidine nucleosides.